Osteoarthritis (OA), a non-inflammatory joint disease characterized by degeneration of joint cartilage, can affect one or more parts of the body, including hands and weight-bearing joints such as knees, hips, feet and the spine. When healthy, cartilage allows bones to glide over each other and has a shock absorber function. In osteoarthritis, the cartilage's surface layer breaks down and wears away, which allows the bones under the cartilage to rub together, causing the common OA symptoms of pain, swelling, and loss of motion of the joint. Furthermore, in joints such as the knees, osteoarthritis is often accompanied by loss of viscosity of the synovial fluid, a thick, gel-like substance that cushions the joint and provides lubrication to reduce friction of the bones.
Osteoarthritis is mainly associated with ageing, with a prevalence of approximately 80% in individuals over 65. Despite being a condition that causes most problems to populations after retirement age, osteoarthritis is also rated the highest cause of work loss in the U.S. and Europe. In addition to age, risk factors known to be associated with osteoarthritis include obesity, traumatic injury and overuse due to sports and occupational stresses.
There is currently no cure for osteoarthritis, and available arthritis therapies are directed at the symptomatic relief of pain, and at improving, or at least maintaining, joint function. Generally, pain relievers such as non-steroidal anti-inflammatory drugs (NSAIDs) or COX-2 inhibitors are used, along with physical therapy. However, in the context of the recent withdrawals of COX-2 inhibitors, physicians are even more limited in their choice of treatment for osteoarthritis.
Viscosupplementation, a procedure involving the injection of gel-like substances (generally hyaluronates or called hyaluronic acid) into a joint to supplement the viscous properties of synovial fluid, has been shown to relieve pain in many osteoarthritis patients who do not get relief from analgesic drugs. The technique has been used in Europe and Asia for several years, but the U.S. Food and Drug Administration did not approve it until 1997. In current procedures of viscosupplementation, hyaluronate preparations are injected to replace or supplement the body's natural hyaluronan, a polysaccharide component of synovial fluid. The injections coat the articular cartilage surface, and thus provide a possible prophylactic barrier for the articular cartilage. However, due to their short lifetime within the joint (about a couple of days), hyaluronate preparations currently available have only limited long-term benefit to the patient and require injection of large quantities of the preparation and/or repeated injections.
Clearly, there is a need for materials with improved performance for use in viscosupplementation for the treatment of osteoarthritis and other conditions affecting weight-bearing joints. In particular, materials with long lifetimes within injected biological fluids or tissues, such as joints, are highly desirable.